[heap] Introduce enum of garbage collection reasons.

src/heap/incremental-marking.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/conversions.h"
 #include "src/heap/gc-idle-time-handler.h"
@@ skipping 479 matching lines @@
       if (CodeStub::MajorKeyFromKey(key) == CodeStub::RecordWrite) {
         Object* e = stubs->ValueAt(i);
         if (e->IsCode()) {
           RecordWriteStub::Patch(Code::cast(e), mode);
         }
       }
     }
   }
 }
 
-
-void IncrementalMarking::Start(const char* reason) {
+void IncrementalMarking::Start(GarbageCollectionReason gc_reason) {
   if (FLAG_trace_incremental_marking) {
     int old_generation_size_mb =
         static_cast<int>(heap()->PromotedSpaceSizeOfObjects() / MB);
     int old_generation_limit_mb =
         static_cast<int>(heap()->old_generation_allocation_limit() / MB);
     heap()->isolate()->PrintWithTimestamp(
         "[IncrementalMarking] Start (%s): old generation %dMB, limit %dMB, "
         "slack %dMB\n",
-        (reason == nullptr) ? "unknown reason" : reason, old_generation_size_mb,
-        old_generation_limit_mb,
+        Heap::GarbageCollectionReasonToString(gc_reason),
+        old_generation_size_mb, old_generation_limit_mb,
         Max(0, old_generation_limit_mb - old_generation_size_mb));
   }
   DCHECK(FLAG_incremental_marking);
   DCHECK(state_ == STOPPED);
   DCHECK(heap_->gc_state() == Heap::NOT_IN_GC);
   DCHECK(!heap_->isolate()->serializer_enabled());
 
   HistogramTimerScope incremental_marking_scope(
       heap_->isolate()->counters()->gc_incremental_marking_start());
   TRACE_EVENT0("v8", "V8.GCIncrementalMarkingStart");
@@ skipping 766 matching lines @@
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 
 }  // namespace internal
 }  // namespace v8